The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: Bill Parker on December 05, 2020, 01:45:37 PM
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I encountered an interesting problem with my 1984 R65 while trying to use the shorting method to sync the carbs. I find it almost impossible to set the throttle such that the engine holds 2500 rpm. It either revs to 3500 or drops to 1500, but won't stay at 2500. Setting it at 3500 and shorting one side yields a progressive drop to 1500 which then fails to regain 3500 when the short is removed. Is this normal or do I have problems with carb settings or the advance mechanism? Thanks.
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This one has electronic ignition and it is advised not to use the shorting method.
Mine ran ok with slightly leaking choke gaskets, heavy floats and a leaky carb top! With fully rebuilt carbs she is very smooth though. They will run around idle with a multitude of problems. My ignition was also several degrees retarded and the engine didn't want to stop.
What caused you to try and balance the carbs? If it was hanging onto revs, then worn advance is said to do that. I'd like to know when the carbs were last overhauled first though!
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I am pretty sure its ok to short the secondary out
What you definitely DO Not want to do is kill the cyl by removing the plug wire
I think the manometer method is safer
That spark can knock the crap out of you :beehive:
Kind of sounds like you have other issues going on
Sticky advance or carburetor issues
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I think you may be aiming a little high at 2500 rpm. The objective is to balance the throttle cables pulling at the same time so any speed above idle will work and the adjustment will be more sensitive at say 1500 rpm. Worth a try.
As an insight into the problem, whatever revs you use to do the balance, the carbs will still be on the idle circuit because the engine is under no load. So the idle circuit including the transition ports is the place to look for issues.
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The carbs were completely overhauled a year ago. I resync the carbs after every valve adjustment and usually use a vacuum device. However I watched a video in which Matt Parkhouse advocated using the shorting method to balance cylinder power instead of vacuum. Since my R65 is a bit more "vibration" prone compared to my other BMW, I'm always looking for a way to make it smoother. I was just asking to see if any other R65 owners had noticed the same RPM instability between idle and ~3000 or if this was an indication of a problem.
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The plug shorting approach to carb balancing is a hangover from days gone by. You can build your own manometer for under $10 or buy a set of gauges or sticks for under $100. Following a post by another member I am getting ready to build an Arduino powered days total carb balancer. It will not work any better than a couple of drink bottles and a few metres of hose and it certainly won't cause world peace to break out, but it is an interesting and cheap project.
The problem is that modern motorcycle engines (yes even R65s) are tuned for a far higher specific output than Grandpa's Indian with 6.5 to 1 compression and teeny little carbs.
The R65 has such small throttle opening at idle you need to have all the planets line up by trying to balance the carbs by running the thing alternatively on single cylinders.
And in any event, that will (if you succeed) only balance at idle. Don't know about you but I am more interested in the balance at moderate opening than I am in the idle balance.
All that said, your problem sounds like a vacuum leak to me. How old are the rubber trumpets connecting the carbs to the cylinder heads? And if they have been replaced, are they tight?
I set ignition timing at 3,500rpm and care not what the idle ignition timing is.
I do set carb balance at idle initially, but then I look at what is happening at progressively larger throttle openings and adjust accordingly.
Oh, and I do valve lash before doing either.
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I encountered an interesting problem with my 1984 R65 while trying to use the shorting method to sync the carbs. I find it almost impossible to set the throttle such that the engine holds 2500 rpm. It either revs to 3500 or drops to 1500, but won't stay at 2500. Setting it at 3500 and shorting one side yields a progressive drop to 1500 which then fails to regain 3500 when the short is removed. Is this normal or do I have problems with carb settings or the advance mechanism? Thanks.
I think I understand what your asking now
Yes
It does seem like it is difficult to lock the throttle to a specific rpm in the range you speak of
But I don't know about the RPM not recovering after spark is restored
Its possible it all has something to do with the CV type carbs
The throttle is very sensitive with out a load on the engine
Does it run fine other wise
As far as the vibration
Make sure your motor mounting bolts are torqued up to 68nm or 50lb/ft
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...my R65 is a bit more "vibration" prone compared to my other BMW...
The R65 is known to have a bit more vibration at certain RPMs than the other Beemers and got a bit of bad press about it at the time.
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On the vibration I had some success by using non standard torque settings. I had noticed that the mono model had lower torque settings which I tried and it made the engine feel smoother in every day use by pushing the vibration period up the rev range. The period of vibration is a resonance between engine and frame and the theory goes that the coupling between engine and frame can influence the resonance. For example it's well known that the very same engine in a different frame can result in very different amounts of vibration. The other option is rubber front engine mounts although they are said to affect the handling. Even the front rubber mounts don't isolate the engine from the frame, they just change the coupling which for me confirms the theory that different torque settings can have an affect. It's a free experiment to try.
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I had the vibration issue when i first got my '81 R65 in 01/81, around the 4200-4500 rpm area .
I installed a Luftmeister rubber forward engine mount isolator kit, no difference in vibration level .
Seems like at 95,000 miles I seriously can say I cannot detect any increase in vibratio0n level at those rpm levels .
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On the vibration I had some success by using non standard torque settings. I had noticed that the mono model had lower torque settings which I tried and it made the engine feel smoother in every day use by pushing the vibration period up the rev range. The period of vibration is a resonance between engine and frame and the theory goes that the coupling between engine and frame can influence the resonance. For example it's well known that the very same engine in a different frame can result in very different amounts of vibration. The other option is rubber front engine mounts although they are said to affect the handling. Even the front rubber mounts don't isolate the engine from the frame, they just change the coupling which for me confirms the theory that different torque settings can have an affect. It's a free experiment to try.
That is what I have noticed also
When I ran the mounts at a lower torque the vibration was softer below 4000 to 4300 ish RPM but harsher above that
I now have them tight and find the vibs are less above and a little more below. I find this more comfortable
I also have a 37/11 final drive and I am sure that has an effect on it also
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Thanks for all the advice. I found that one carb was leaking fuel past the float valve at idle, enough to cause that side to run very rich. A removal and thorough cleaning/adjustment seems to have solved that problem. But now my Harmonizer (vacuum sync) has broken and I'm waiting on a Twinmax to re-sync.
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Hey I got one right for a change? 8)
Regarding shorting secondary coils, I think this will result in a higher primary current going in. Instead of building current to saturate the coil and then levelling out on primary resistance, it also now has to supply the secondary which takes current whilst charging (when is shouldn't). I don't know the exact characteristics of these things, but short on a secondary means increased current on the primary. I'm also not sure what the current does when when the transistor goes off with a shorted secondary. It probably reduces and if so, not a problem. Surprisingly I can't find this kind of measurement on the web.
Since the primary probably current goes up and the transistor has fixed instantaneous and long term limits; it may fail immediately or after several cycles depending on components. Contacts are harder to break - they would normally weld in after abuse in say a relay, except this big cam comes and forces them open rather than a spring.
I'd be interested if someone has a graph of primary vs secondary currents when normally loaded AND when the secondary is shorted out. I think it goes up in a nasty way whilst saturating.
EDIT:- I found something, but on modern transistor ignitions which will have protection (current limit). But yes, a shorted secondary makes the average current in the primary go up. Enough to blow up one of our simple transistor ignitions? I don't know.
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Regarding shorting secondary coils, I think this will result in a higher primary current going in. Instead of building current to saturate the coil and then levelling out on primary resistance, it also now has to supply the secondary which takes current whilst charging (when is shouldn't).
I'd be interested if someone has a graph of primary vs secondary currents when normally loaded AND when the secondary is shorted out. I think it goes up in a nasty way whilst saturating.
Remember with a dual tower coil the secondary is not completely shorted when only one side is grounded
But I think you may be correct
You got me curious
Not sure if it is enough to overload the ICU
I have a trace of the normal current in the secondary
I will have to get the scope out this weekend and see how high it does go when shorted
I think it would be safe to say "Do not completely short or open the secondary" :beerchug:
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While the average primary current may change I can't see there is any change to the maximum value of primary current as that is limited by the primary resistance. What shorting the secondary might do is change the inductance so that the rate of rise of the primary current and therefore the measured average is different. I doubt it's a big deal in terms of current but there may be other transient effects.
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All good 8)
Measurements anticipated :lurker:
I'm not sure why our brains deterioate after 18 years or so, it seems a complete waste since we live to (fill in latest speculation here) (around 90) and it can't all be crammed in that time. Mr Darwin was right and I hope we override him in the future i.e we each hit our own wall and someone else puts a hole in it. Which is a really good thing. The trouble is my depleting cells can't add it and it just gets lost. I suppose if the collective knowledge becomes singular, then that might be a very dangerous thing - in the the wrong hands / brain.
So yes, interested in what your 'scope shows, since I haven't reached an override yet :thud:
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Sorry about not getting back sooner
Needed a new Battery and I waited until I had it apart to test the current draw
So
It appears shorting the secondary makes little difference on primary current draw
As a matter a fact it pulls slightly more when it is running than it does during cranking with the plugs shorted
About the only difference is saturation time
FYI
This is not a stock Bosch system
It is has the standard bean can but I am using a 1.5 ohm Dyna coil and a GM Delco HEI ignition module (used in 74 and on GM cars and trucks)
The first screen shot is
ignition on
coil powered up
not cranking
both secondary's grounded
Thats about 4.4 amps
According to Ohms law the ICU must be current limiting
I know if I install a ,7 ohm coil the Icu gets hot
Thats why I went back to a brown coil
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This is cranking
both secondaries grounded
No higher amp draw
You will notice the saturation slower than when one side is making spark as in the next picture
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here is one side shorted one side sparking under compression
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And finally just idling
Both cylinders firing
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Thanks for the full report. You promotion will show in your paycheck at the end of the month :tekst-toppie:
Can't find a definitive spec sheet, but from http://nebula.wsimg.com/5956cdbfbf7fc2e9bc4c33682dbb7427?AccessKeyId=967E22DE049163134A29&disposition=0&alloworigin=1
But that is not all that the HEI module does. The
HEI module electronically limits the peak coil current to around 6 Amps,
It also makes other adjustments to dwell, so the fact that nothing has gone 'bang!' on your custom system is expected. The stock electronic switch I am sure is not intelligent and is likely to draw strange currents and indeed follow in Mr Fawkes plan..... :flamethrowingsmiley:
?
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Can't find a definitive spec sheet, but from http://nebula.wsimg.com/5956cdbfbf7fc2e9bc4c33682dbb7427?AccessKeyId=967E22DE049163134A29&disposition=0&alloworigin=1
Fascinating article on the HEI module. You have to wonder why aftermarket electronic ignitions are so expensive when something as cheap as a HEI module can do everything needed.
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Can't find a definitive spec sheet, but from http://nebula.wsimg.com/5956cdbfbf7fc2e9bc4c33682dbb7427?AccessKeyId=967E22DE049163134A29&disposition=0&alloworigin=1
Fascinating article on the HEI module. You have to wonder why aftermarket electronic ignitions are so expensive when something as cheap as a HEI module can do everything needed.
Unfortunately I do not get all of the benefits the HEI has to offer because i am using the hall sensor instead of the reluctor that the HEI normally uses
The main one is the longer dwell at higher RPM and the fact the coil will power up when the engine is not turning
That is why I have to stay with the 1.5 ohm coil :'(
I need to get at rid of the hall and figure out how to mount the reluctor in the can ;)